In October, the Centers for Disease Control and Prevention announced that the number of people living with HIV in the United States but who haven't been tested and diagnosed fell from 25% in 2003 to 21% in 2006.

The decrease matters: You can't get treated for HIV if you're unaware you have it—and treatment extends life and health. People who know they're positive are also less likely to transmit the virus.

There's a footnote, though: The total number of HIV-positive Americans continues to rise.  So the fight for prevention continues too.